Liu Shuang, Long Mengqiu, Wang Yun-Peng
School of Physics and Electronics, Hunan Key Laboratory for Super-microstructure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha 410083, People's Republic of China.
Nano Lett. 2023 Aug 23;23(16):7427-7433. doi: 10.1021/acs.nanolett.3c01851. Epub 2023 Aug 7.
Raman spectroscopy is one of the most useful experimental tools for studying elementary excitations in two-dimensional (2D) materials. The Raman scattering due to phonons was widely employed for detecting structural evolutions, especially those caused by magnetic phase transitions in 2D magnets. A first-principles theory of the Raman scattering effect caused by magnons is still lacking. We theoretically study the magnon Raman effect in 2D magnet CrI. We propose a first-principles method and have calculated the intensity of circularly polarized Raman signals due to different magnon modes in the CrI monolayer and bilayers. The calculated Raman intensities due to magnons in the CrI monolayer and the rhombohedral bilayer are consistent with the selection rule deduced from the magnon pseudoangular moment and the parity of magnon modes. We also find that the selection rule is violated in the symmetry-broken monoclinic bilayer due to interlayer coupling.
拉曼光谱是研究二维（2D）材料中基本激发的最有用的实验工具之一。由声子引起的拉曼散射被广泛用于检测结构演变，特别是二维磁体中由磁相变引起的结构演变。目前仍缺乏关于由磁振子引起的拉曼散射效应的第一性原理理论。我们从理论上研究了二维磁体CrI中的磁振子拉曼效应。我们提出了一种第一性原理方法，并计算了CrI单层和双层中不同磁振子模式引起的圆偏振拉曼信号的强度。计算得到的CrI单层和菱面体双层中磁振子引起的拉曼强度与从磁振子赝角动量和磁振子模式宇称推导出的选择规则一致。我们还发现，由于层间耦合，在对称性破缺的单斜双层中选择规则被违反。
